While true, using a browser for mining doesn't require the user to have any cryptocurrency, or even know what cryptocurrency is. It also has a similarly opaque cost to them (in the form of electricity).
Brave is getting around that with built-in support for their "Basic Attention Token" which will be rewarded to users just for using their browser.
It will be interesting to see how it works out.
Personally I am just sad that it takes so much energy to maintain the current cryptocurrency networks and they are already too slow for really interesting stuff -- which is why I wouldn't want to add more waste by mining in a browser :).
